1. Field of the Invention
The present invention relates to a color signal processing apparatus, a method of the same and a camera apparatus which perform a white balance processing of a color signal of an image taken by a solid-state imaging device such as a.charge coupled device (CCD).
2. Description of the Related Art
When taking an image by using a solid-state imaging device such as a CCD, a white color in an objective image becomes reddish in results of the image taken under an environment of low color temperature like at indoors, while it becomes bluish in results of the image taken under an environment of high color temperature like at outdoors.
The color temperature here is defined as a temperature of blackbody (K) having the same chrominance as a light source for a test.
When using a camera apparatus employing such a solid-state imaging device to reproduce a white color from the objective image to appear as an achromatic color in the reproduced image, if the color temperature of the light source changes, the input color white moves along a blackbody emission curve (blackbody locus 2) in accordance with changes of a color temperature as shown in FIG. 1A. In this case, an automatic white balance (AWB) processing is performed to match a white portion of the objective image, that appears to be colored because of the color temperature changes of the light source, to an achromatic white color of a reproduced image.
In the automatic white balance processing, in order to remain the colors as they are for the portions originally not being white, it is necessary to prevent erroneously performing white balance processing to any color that was not white in the original objective image. Therefore, a camera apparatus sets a pull-in limit region 3, shown in FIG. 1B, which limits a range the white balance operation is performed. The white balance processing is performed only when white color is positioned within the pull-in limit region 3, while the white balance operation is not performed when it is positioned outside the region 3.
Conventionally, the pull-in limit region 3 is set to be a simple rectangular shape, as shown in FIG. 1B. As a result, a program volume for processing the white balance can be reduced compared with a case with a complex shape.
However, when using the rectangular pull-in limit region 3 as shown in FIG. 1B for the automatic white balance processing in the same way as the above camera apparatus, the automatic white balance processing is performed with respect to colors outside the changing direction of the color temperature being along with the blackbody emission curve 2, as shown in FIG. 1C, and the colors are made to be different from the original. In an example shown in FIG. 1C, the automatic white balance processing is performed to magenta (Mg).
To overcome the disadvantage, when using a pull-in limit region 5 which is combination of a plurality of rectangles to be along with the blackbody emission curve 2, as shown in FIG. 2A, the automatic white balance processing is not performed to colors outside the change direction of the color temperature along with the blackbody emission curve 2, and, for example, magenta can be remained as it is, as shown in FIG. 2B.
However, in the methods shown in FIGS. 2A to 2C, the pull-in limit region 5 has six boundary lines, as shown in FIG. 2C, so that when judging if the objective color is inside the pull-in limit region 5 or outside, it is necessary to judge that on which side the objective color is positioned with respect to six boundary lines. Therefore, there is a disadvantage that a volume of the program to perform the automatic white balance processing becomes large and the processing time becomes long.
Another methods can be considered which stores all the combinations of R gain and B gain being positioned at predetermined intervals on the blackbody emission curve, judges if an objective color is one of the stored combinations or not, and determines whether or not to perform the automatic white balance processing. In this methods, more highly precise automatic white balance processing can be realized, however, as same as the case in FIGS. 2A to 2C, there is a disadvantage that the program volume is large and the processing time is long.
An object of the present invention is to provide a color signal processing circuit, a method of the same and a camera apparatus, which can perform a highly precise automatic white balance processing with a small program volume.
According to the present invention, there is provided a color signal processing circuit comprising: an amplification circuit having three gains for amplifying a color signal of red, green and blue color signals and amplifying the red, green and blue color signals, the red green and blue color signals being generated from an image signal taken by a solid-state imaging device by a color separation; a pull-in determination circuit for judging whether or not the color signal in a two dimensional coordinates for defining the color is positioned within a first pull-in limit region showing a color adjustment region and a second pull-in limit region defined in the first pull-in limit region and contained an origin of the two dimensional coordinates, and determinating the pull-in of a color shown by the signal into a white color defined as the origin of the two dimensional coordinates; and a gain adjustment circuit for adjusting the gain of the amplification circuit, to thereby pull-in the color shown by the color signal determined the pull-in into the origin of the two dimensional coordinates.
Preferably, the color signal processing circuit further comprises an integration circuit for integrating the color signal to generate an integrated color signal.
The pull-in determination circuit judges whether or not the integrated color signal in the two dimensional coordinates is positioned within the first pull-in limit region and the second pull-in limit region, and determines the pull-in of a color shown by the integrated color signal into the white color defined as the origin of the two dimensional coordinates. The gain adjustment circuit adjusts the gain of the amplification circuit, to thereby pull-in the color shown by the integrated color signal determined the pull-in into the origin of the two dimensional coordinates.
Preferably, the integration circuit integrates the color signal, every field to generate the integrated color signal.
The two dimensional coordinates may be defined by a first axis showing (R+Bxe2x88x922G), where R represents red, B represents blue and G represents green, and a second axis showing (R-B).
Preferably the integration :circuit integrates an (R-G) color signal and a (B-G) color signal every field to generate an (R-G) integrated color signal every field and a (B-G) integrated color signal. The pull-in determination circuit calculates the (R-G) integrated color signal and the (B-G) integrated color signal to obtain an (R-B) integrated color signal and an (R+Bxe2x88x922G) integrated color signal, and judges whether or not the (R-B) integrated color signal and the (R+Bxe2x88x922G) integrated color signal in the two dimensional coordinates for defining the color is positioned within the first pull-in limit region and the second pull-in limit region, and determines the pull-in of a color shown by the integrated color signal into the white color defined as the origin of the two dimensional coordinates. The gain adjustment circuit adjusts the gain of the amplification circuit to thereby pull-in the color shown by the integrated color signal into the origin of the two dimensional coordinates.
The first pull-in limit region is defined as a first rectangular shape which are defined by first to fourth lines, the first and second lines being parallel to each other and being positioned both sides of a blackbody emission curve in the two dimensional coordinates and passing the origin, and the third and fourth lines being parallel to each other and perpendicular to the first and second lines, and the second pull-in limit region is defined as a second rectangular shape and is smaller than the first pull-in limit region, the second rectangular shape being defined by fifth to eighth lines, the fifth and sixth lines being parallel to each other and to the first and second lines of the first pull-in limit region, and being respectively positioned between the first line and the blackbody emission curve and between the blackbody emission curve and the second line, the seventh and eighth lines being parallel to each other and perpendicular to the fifth and sixth lines, the fifth line of a upper position being defined as a first reference line and the sixth line of a lower position being defined as a second reference line.
The color shown by the color signal may be varied to another color shifted from the white color along a blackbody emission curve in the two dimensional coordinates in response to the change of a color temperature.
Alternatively, the color shown by the integrated color signal may be varied to another color shifted from the white color along the blackbody emission curve in the two dimensional coordinates in response to the change of a color temperature. The first and second lines defining the first pull-in limit region are parallel to a tangential line of the blackbody emission curve at the origin.
Preferably, the solid-state imaging device is a charge coupled device.
In the color signal processing circuit of the present invention, only when two dimensional coordinates of the color signal is positioned inside the first pull-in limit region in the two dimensional coordinates and also is positioned inside the second pull-in limit region, the processing for pulling in the color indicated by the color signal to the origin is performed.
The second pull-in limit region is closer to the blackbody emission curve compared with the first pull-in limit region. Therefore, compared with the case only using the first pull-in limit region, it can prevented to pull in colors other than white to white more correctly.
According to the present invention, there is also provided a method for processing a color signal, including the steps of: amplifying a color signal of red, green and blue color signals by an amplification circuit having three gains for amplifying the red, green and blue color signals, the red, green and blue color signals being generated from an image signal taken by a solid-state imaging device by a color separation; judging whether or not the color signal in a two dimensional coordinates for defining the color is positioned within a first pull-in limit region showing a color adjustment region and a second pull-in limit region defined in the first pull-in limit region and contained an origin of the two dimensional coordinates, and determinating the pull-in of a color shown by the color signal into a white color defined as the origin of the two dimensional coordinates; and adjusting the gain of the amplification circuit, to thereby pull-in the color shown by the color signal determined the pull-in into the origin of the two dimensional coordinates.
According to the present invention, there is further provided a camera apparatus comprising: an imaging means including a plurality of solid-state imaging devices for generating an analog image signal of an object; an A/D converter converting the analog image signal to a digital image signal; a primary-color separation circuit for separating the digital converted image signal to a red (R) color signal, a green (G) color signal and a blue (B) color signal; an amplification circuit having three gains for amplifying a color signal of red, green and blue color signals and amplifying the red, green and blue color signals; a pull-in determination circuit for judging whether or not the color signal in a two dimensional coordinates for defining the color is positioned within a first pull-in limit region showing a color adjustment region and a second pull-in limit region defined in the first pull-in limit region and contained an origin of the two dimensional coordinates, and determinating the pull-in of a color shown by the color signal into a white color defined as the origin of the two dimensional coordinates; and a gain adjustment circuit for adjusting the gain of the amplification circuit, to thereby pull-in the color shown by the color signal determined the pull-in into the origin of the two dimensional coordinates.